Catalyst comprising palladium on silicaalumina treated with a carboxylic acid, method of preparation and isomerization process using same



May 17, 1960 HYDROGEN H. O. FOLKINS ETAL CATALYST COMPRISING PALLADIUMON SILICA-ALUMINA TREATED WITH A CARBOXYLIC ACID, METHOD OF PREPARATION,AN

ISOMERIZATION PROCESS USING SAME Filed Sept. 18, 1958 S'ILICA- ALUMINACATALYST SUPPORT CALCINED TO LOW WATER CONTENT WITHOUT DAMAGING GELSTRUCTURE IMPREGNATE WITH 5-307. SOLUTION OF A LOW MOL. WI

CARBOXYLIC ACID I DRY AT 225 3565 IMPREGNATE WITH SOLUTION OF REDUCIBLEPALLADIUM COMPOUND I I DRY AT 225-35o E FORM INTO PELLETS REDUCE T0METALLIC PALLADIUM AT 750 -975 F HIGHLY ACTIVE CATALYST PRODUCT PRE PARA TION AND A CT! VAT/ON OF I S OME RIZ A TION CATALYST SOLUTION OFREDUCIBLE IMPREGN ATE WITH PALLADIUM COMPOUND, CONTAINING 5-3o/. OFA LOWMOL. wT

CARBOXYLIC ACID CONDITION AND EXTRUDE INVENTORS H/LLIS 0. FOLK/NS BYELMER MILLER A TTORNE United States Patent CATALYST COMPRISING PALLADIUMON SILICA- ALUMINA TREATED WITH A CARBOXYLIC ACID, METHOD OF PREPARATIONAND ISOM- ERIZATION PROCESS USING SAME Hillis O. Folkins, Crystal Lake,and Elmer L. Miller,

Cary, 111., assignors to The Pure Oil Company, Chicago, 111., acorporation of Ohio Application September 18, 1958, Serial No. 761,713

11 Claims. (Cl. 260483.65)

passing the feed stocks over a catalyst under moderate temperatureisomerization conditions. When paraflin hydrocarbons are isomerized inthis manner, a mixture of hydrogen and the hydrocarbon in ahydrogen/hydrocarbon mol ratio in the range from about 0.5 to 5.0, is

passed over a composite catalyst at a pressure within the range fromabout 100 to 1,000 p.s.i.g. and a 'temperature within the range fromabout 600 to 800 F. The most effective composite catalyst forisomerization of normal paraffin hydrocarbons under the conditions justdescribed consists of an acidic silica-alumina support having depositedthereon from 0.01 to 1.0 wt. percent of palladium. In accordance withthis invention, it has been found that the treatment of thesilica-alumina sup port with a 5-30% solution'of a low-molecular-weightcarboxylic acid, such as acetic acid, either prior to or concomitantlywith the deposition of palladium on the support, produces anisomerization catalyst having supenor isomerization activity. g I

It is, therefore, one object of this invention to provide an improvedprocess for the preparation of a highly active isomerization catalyst.

Another object of this invention is to provide a highly activeisomerization catalyst capable of effecting the isomerization oflow-molecular-weight normal parafiins to isoparaflins in high yield.

Another object of this invention is to provide an improved process forthe isomerization of hydrocarbon feed stocks consisting predominantly oflow-molecularweight normal parafiins.

A feature of this invention is the provision of a proces for thepreparation of highly active isomerization catalysts in which asilica-alumina support is treated with a dilute solution of alow-molecular-weight organic acid,

such as acetic acid, and with a solution of a reducible palladiumcompound, and the impregnated support reduced with hydrogen at elevatedtemperatures to produce a highly active catalyst.

Another feature of this invention is the provision of an improvedisomerization catalyst consisting of 0.0l-1.0 wt. percent of palladiumon silica-alumina, containing 50-95% silica, in which the silica-aluminasupport has been treated with a dilute aqueous solution of alowmolecular-weight organic acid, such as acetic acid, either prior toor concomitantly with the impregnation of the support with a palladiumcompound.

A further feature of this invention is the. provision of an improvedprocess for isomerization of normal paraflin in the range from about600-800 F., over a catalyst.

consisting of 0.01-1.0 wt. percent palladium on silicaalumina,containing 50-95% silica, which catalyst has been treated with alow-molecular-weight organic acid, such as acetic acid, prior to orconcomitantly with the deposition of palladium thereon.

Other objects and features of this invention will become apparent fromtime to time throughout the specification and claims as hereinafterrelated.

In the accompanying drawings, there is set forth a fiow diagram of apreferred embodiment of our process for preparing an improvedisomerization catalyst.

According to-this invention, it has been found that the effectiveness ofa palladium-promoted, silica-alumina, composite isomerization catalystcan be enhanced by treating the silica-alumina support with a solutionof a low-molecular-weight organic acid, such as acetic acid, eitherprior to or concomitantly with the deposition of palladium thereon. Inthe preparation of catalyst compositions in accordance with thisinvention, the palladium metal is incorporated in the silica-aluminasupport by impregnation of the support with a solution of a reduciblepalladium salt, such as the chloride or nitrate, or with a solution of amixed palladium salt, such as ammonium chloropalladite. The preparationof the supported catalyst is generally carried out by impregnating thesupport with an aqueous solution of palladium chlo- I ride, sometimescontaining small amounts of an inorganic acid such as hydrochloric acid.In our process, the catalyst support is wetted with a dilute solution offrom about 5 to 30% of acetic acid in water or other suitable solvent.The catalyst support used is a silicaalumina, containing 50-95 wt.percent silica, which has been precalcined to produce a low watercontent without damaging the gel structure. Precalcination of thesupport is preferably limited so that about 0.75-1.00 wt. percent ofwater remains on the surface of the support, and/or in the structure ofthe support. Alternately,

,milder precalcination may be employed whereby the amount of water lefton or in the support is as high as 3-4 wt; percent. The catalyst supportwhich has been wetted with acetic acid solution is then dried at about225 -350 F., preferably about 230 F. The catalyst support is thenimpregnated with a solution of a reducible palladium salt. Theimpregnated catalyst is dried at about 225 -350 F., and is formed intopellets by a suitable pelleting machine. Alternately, the impregnatedcatalyst may be conditioned for extrusion either by adjustment of thewater content, generally to a range of 50-65%, or by the addition ofinert lubricants or binders. The catalyst mass then is extruded and cutinto suitable lengths. The catalyst so formed is dried, if necessary,and is activated by reduction with hydrogen at a temperature of about750 to 975 F. The catalyst which is thus produced has a concentration ofpalladium metal thereon which is determined by the concentration of thesolution of palladium salt used to impregnate the catalyst support.

As an alternative method of preparing the catalyst, the acid-treatingstep and impregnation with palladium salt may be combined. In thismethod the palladium salt is much more active catalyst and produceshigher yields of isoparaflins than does a catalyst prepared in the samemanner without the acid treatment of the catalyst support."

Patented May 17, 1960 When'hydrogen and C5-C normal paraflins in ahydrogen/hydrocarbon mol ratio Within'the range'of'about" 0.5-5.0 arepassed over a catalyst prepared and activated as above-described, atatemperatureof about 600-800 F1, a pressureof"100l000 p.s.i.g.;, and aliquid volume hourly spacevelocityof 0.5 1010.0, ayie'ld ofisoparafiinsisobtained which .is much" higher than isJobtained using 1 a catalystOfthesame composition which has nothad the acidtreatment:

The. following non-limiting "examples illustrate the A commercialsilica-alumina cracking catalyst, conmining-13% aluminaand 87% silica,was driedat 400 F. foraperiod of .3 hours A 250 g.- portion of thecatalyst support was then impregnated at 120 F. with asolutionof 1.4 g.of. palladium chloride in 250cc. of a water solution which contained 25.cc; of glacial'acetic acid. The amount of solution used was justsufiicient to fill the pores of the catalyst support. The impregnatedvcatalyst mass wasdried'at 230 F. and .fiormed into pellets. Thecatalyst. pellets were then activated by heating at 975 F. in aJcur-rentof hydrogen .for a period of :16 hours to reduce the palladium salt tometallic palladium in .a highly active form.. After reduction with.hydrogen, the catalyst pellets contained 0.33wt. percent palladium.Thecatalyst thus prepared wasevaluated in the isomerization ofn-pentane.

Hydrogen and n-pentane in a 1:1 mol ratio were circulatedfover thecatalyst at .a temperature of 703 F., a pressure of 500 p.s.i.g., and aliquid volume hourly. space velocity of 3.0. The liquid volume hourlyspace velocity is defined as liquid volume of hydrocarbon fed per hourper unit volume ofeftective catalyst bed.. Under the above reactionconditions, isopentane was obtained in a yield 'of 50.5% and selectivityof 98.8%. When the reaction temperature was raised to 724 F., using thesame catalyst and the same reaction conditions, the isopentane yield wasincreased to 56.3% but the selectivity decreased slightly to 98.0%.

In another experiment the catalyst was prepared .using theabove-described procedure except that sutficient palladium chloridewasused in the impregnatingsolution to produce a palladium concentrationonthe catalyst of 0.40% and 1 the impregnating. solutioncontained .twicetheof 3.0, was passed over the catalyst at 700 F. An iso-- pentane yieldof 54.8% was/obtained. When ;the.isomeiization reaction was repeated ata temperatureof 725 F., the isopentane yield increased to 59.8%.

EXAMPLE II A commercial silica-alumina cracking catalyst, containing 87%silica and 13% alumina, was dried to produce a low water content withoutdestroying the gel structure. A 250-gram quantity of this catalystsupport was then impregnated with a solution of 1.4 g. of palladiumchloride in 250 cc. of 0.90 N hydrochloric acid. The impregnatedcatalyst mass was dried at 230 F., iormedinto pellets, and activated byreduction with hydrogen at 975 F. The catalyst thus produced wasevaluated as in Ex ample I for activity in the isomerization ofn-pentane. Hydrogen and n-pentane in a m ol ratio ofl l, a pressure of500 p.s.i.g., and a liquid volume hourly space velocity of 3.0, werecirculated over the catalyst at 700 The yieldof isopentane from this runwas 39.5

43 Another catalyst sample was prepared using a solution of palladiumchloride in 1:34N hydrochloric acid'to' produce a palladium metalcontent on the catalyst support (87/13 silica-alumina) of 0.40%. Thecatalyst was dried, pelleted, and reduced -with hydrogen at 975 F. asabove-described. 'I'his"cata1yst' was evaluated for act'rvity in the:isomerization of .-n=,pentane,.under j the, same conditionsofpressure;hydrocarbon/hydrogen .ratio .and flow rate; At. 7 00? 'F.', the .yieldof isopentanerusing this catalyst sample was 41.5

From the above examples, it is; seen that the-treatmentofasilica-alumina catalyst supportwith-a5-'-30% solution of acetic acid'producesa catalyst ofhigheractivity than is produced when the catalystis merely impregnated with a solution of apalladium salt notcontaim'ngacetic acid. While the-processzh'as been described withspecial emphasis upon the use of acetic acid, it should be understoodthat other C -C carboxylic acids, suchas formic acid, propionic acid,butyric acid, oxalic, acid,.malonic acid; succinic acid, and valericacidmayv be used. It should als'obe noted that the acid solution maybeapplied to the catalyst support prior to impregnation of the supportwiththe palladium-containing solution. When this procedure is followed; thecatalyst support is first treated with theacidsolution and dried at atemperatureiof about 225 350 The catalyst is then impregnated with anaqueous solution of palladium chloride, either. with or without"addedihydrochloric acid, and the impregnated catalyst reduced with.hydrogen .at an elevated tempera ture; The resulting catalyst is of.substantially higher activity than the'catalyst which is obtainedwithout the use of the carboxylic acid treatment.

The operating conditions for isomerization of normal paraffinhydrocarbons using the catalyst of this invention are normally selectedso that denegeration .or fouling of the .catalyst doesnot occur.However, the catalyst may become fouled after extremelylong processperiods. and thus may require reactivation or regeneration about once ayear. The regeneration procedure which is followed is one in which thecatalyst is oxidized to eliminate carbon and: other deposits'fromthecatalyst'and then reduced. The oxidation and'reduction temperaturesused are such that the catalystis not subjected to sintering and theactivity of thecatalystremains-high. The catalyst is oxidized using airor oxygen at a temperature in the rangeg'from about700 to 950 F., with atemperature of 950 F. Whenthe catalyst treated with: acetic acid, or 4other C -C carboxylic acid in accordance with thisinvention, isregeneratedafter an extended period of use, the activity'of the catalystmay bereducedup to about 4% on each. regeneration. However, the:catalyst can be regenerated four or five times and: still have anactivity substantially higher thanthat of a catalyst which did notreceive theiinitial acetic acid treatment- In isomerizing-normalparaflinhydrocarbons containing four-to seven carbon atoms-per molecule, inaccordance with this invention, the catalyst used is prepared bytreating asilica-alumina support with acetic acid or other C -Ccarboxylic acid'either prior to or concomitantly with theimpregnation ofthe silica-alumina support with a palladium-containing solution. Thesilica-alumina sup port which is 'used must be of 'an acidic nature andmust contain from 50 to silica, with 70-'90% silica being preferred. Thecatalyst supportis provided with palladium in a concentration of from0.01 to 1.0%", with a concentration of 0.1 to 0.8% being preferred. Inthe isomerization of difierent C '-C ,normal parffin hydrocarbons, theoptimum isomerization conditions are diftercnt OI d fircnt hydrocarbons,as shown in Table l.

It is apparent that when mixed feed stocks are employed, a compromisemust be efiected in selecting the temperature which is to be used inorder to produce optimum activity and selectivity forthe desiredis'oparaifins without producing substantial amounts of hydrocracking asa concomitant, undesirable side-reaction. The optimum temperature is onewhich in most cases must be determined experimentally in accordance withthe relative proportions of hydrocarbons inthe feed. The maximumefficiency in isomerization of the various C -C hydrocarbons is obtainedby passing the hydrocarbon feed through a suitable fractionating systemto separate the individual hydrocarbons for isomerization under optimumconditions for each hydrocarbon. The products of each isomerization maythen be combined into a single product.

While we have described our invention fully and completely as requiredby the Patent Statutes with special emphasis upon one or more preferredembodiments, we wish it understood that within the scope of the appendedclaims this invention may bepracticed otherwise than as specificallydescribed.

What is claimed is:

l. The method of preparing a hydrocarbon isomerization catalyst whichcomprises impregnating a precalcined silica-alumina catalyst support,containing 50-95 wt. percent silica, with a 5-30% solution of a C -Ccarboxylic acid and a solution of a reducible palladium compound in anamount sufiicient to produce a palladium concentration of 0.01l.'0 wt.percent on the catalyst support, drying the impregnated catalyst supportat about 225-350 E, and reducing the catalyst with hydrogen at 750-975F.

2. A method in accordance with claim 1 in which the catalyst is formedinto pellets after impregnation and drying.

3. A method in accordance with claim 1 in which the catalyst is dried at225 -350 F. after impregnation with the acid solution and beforeimpregnation with the solution of the palladium compound.

4. A method in accordance with claim 1 in which the catalyst support isimpregnated with a single solution containing a reducible palladiumcompound and 5-30 percent of a C -C carboxylic acid.

5. A method of preparing a hydrocarbon isomerization catalyst whichcomprises impregnating a precalcined silica-alumina support, containing50-95 Wt. percent silica, with an aqueous solution of palladium chloridecontaining 530% acetic acid to produce a palladium concentration of0.01-1.0%, drying the impregnated support at 225350 F., and reducing thecatalyst with hydrogen at 750 975? F.

about 0.5-5.0, over a catalyst prepared and activated in accordance withclaim 1.

10. A method of isomerizing C -C normal parafiin hydrocarbons whichcomprises passing hydrogen and a normal paraflin hydrocarbon at atemperature in the range of about 600-800 F., suflicient to effectisomerization, a pressure of about -1000 p.s.i.g., a liquid volumehourly space velocity of 0.5 to 10.0, and a hydrogen/hydrocarbon molratio within the range of about 0.5-5.0, over a catalyst prepared andactivated in accordance with claim 2.

11. A method of isomerizing C -C normal paraflin hydrocarbons whichcomprises passing hydrogen and a normal paraffin hydrocarbon at atemperature in the range of about 600-800 F., sufiicient to effectisomerization, a pressure of about 100-1000 p.s.i.'g., a liquid volumehourly space velocity of 0.5 to 10.0, and a hydrogen/hydrocarbon molratio within the range of about 05-50, over a catalyst prepared andactivated in accordance with claim 5.

References Cited in the file of this patent UNITED STATES PATENTS2,662,861 Riblett et a1 Dec. 15, 1953 2,767,148 Plank Oct. 16, 1956FOREIGN PATENTS 487,392 Canada Oct. 21, 1952

1. THE METHOD OF PREPARING A HYDROCARBON ISOMERIZATION CATALYST WHICHCOMPRISES IMPREGNATING A PRECALCINED SILICA-ALUMINA CATALYST SUPPORT,CONTAINING 50-95 WT. PERCENT SILICA, WITH A 5-30% SOLUTION OF A C1-C5CARBOXYLIC ACID AND A SOLUTION OF A REDUCIBLE PALLADIUM COMPOUND IN ANAMOUNT SUFFICIENT TO PRODUCE A PALLADIUM CONCENTRATION OF 0.01-1.0 WT.PERCENT ON THE CATALYST SUPPORT, DRYING THE IMPREGNATED CATALYST SUPPORTAT ABOUT